This invention relates to an improved carbonaceous heat source and to the catalytic conversion of gaseous by-products, such as carbon monoxide, produced by the combustion of the carbonaceous heat sources to a benign substance. The methods and heat source of this invention are particularly suitable for use in a smoking article such as that described in commonly assigned U.S. Pat. No. 4,991,606. The heat sources of this invention comprise carbon and smaller amounts on a weight basis of a metal species. The heat sources of this invention have low ignition and high combustion temperatures that generate sufficient heat to release a flavored aerosol from a flavor bed for inhalation by the smoker. Upon combustion, the catalytic component of the heat sources converts substantially all of the carbon monoxide to a benign substance.
According to the method of this invention, a carbon component is mixed with a metal species. Upon combustion, the metal species generates in situ a catalyst which converts the carbon monoxide by-product formed by combustion of the heat source to a benign substance. In a preferred embodiment, the metal species and carbon component are mixed together and then formed into a desired shape.
There have been previous attempts to provide a catalyst for the oxidation of carbon monoxide to carbon dioxide. These attempts have not produced a catalyst having all of the advantages of the present invention.
For example, Dale U.S. Pat. No. 4,317,460 discloses an oxidation catalyst adsorbed onto a solid support. The catalyst may be located in either a smoking article or in a filter tip.
Leary et al. Journal of Catalysis, 101, pp. 301-13 (1986) refers to a catalyst for the oxidation of carbon monoxide produced by an internal combustion engine. These catalysts, however, are derived from expensive metals.
Haruta et al., Journal of Catalysis. 115, 301-309 (1989) refers to production of an oxidation catalyst for the low-temperature conversion of carbon monoxide.
Walker et al., Journal of catalysis, 110, pp. 298-309 (1988) refers to an iron oxide-based catalyst for the simultaneous oxidation of carbon monoxide and propane.
It would be desirable to provide an inexpensive heat source which comprises a catalyst for the oxidation of carbon monoxide.
It would be desirable to provide an oxidation catalyst that is active at a broad range of temperatures, i.e., from above room temperature to about those reached in a combusting carbonaceous heat source.
It would be desirable to provide a carbonaceous heat source in which an oxidation catalyst of high activity is generated in situ during combustion of the heat source.
It would be desirable to provide a carbonaceous heat source that has a low temperature of ignition to allow for easy lighting under conditions typical for a conventional cigarette, while at the same time providing sufficient heat to release flavors from a flavor bed.
It would be further desirable to provide a carbonaceous heat source which does not self-extinguish prematurely.
It would be desirable to provide a carbonaceous heat source which liberates virtually no carbon monoxide.